update 273 (fwd)

[Jim Choate <ravage@ssz.com>]

Forwarded message:
>From physnews@aip.org Mon Jun  3 17:03:16 1996
Date: Mon, 3 Jun 96 14:06:02 EDT
From: physnews@aip.org (AIP listserver)
Message-Id: <9606031806.AA07182@aip.org>
To: physnews-mailing@aip.org
Subject: update 273


PHYSICS NEWS UPDATE                         
The American Institute of Physics Bulletin of Physics News
Number 273  May 31, 1996    by Phillip F. Schewe and Ben Stein

SCHRODINGER'S CAT-ION: Physicists at NIST (Christopher
Monroe, 303-497-7415) have experimentally demonstrated the
principles of the famous Schrodinger's cat thought experiment with
a single beryllium ion. In a 1935 paper, physicist Erwin
Schrodinger proposed the cat paradox: put a cat inside a box, add
a container of poison gas which is activated by the decay of a
radioactive atom, and close the box.  Since the radioactive atom
obeys the rules of quantum mechanics and since therefore its state
is indeterminate until measured by an outside observer, opening the
box and observing the atom (a microscopic quantum system)
instantly determines the status of the cat (a decidedly macroscopic,
non-quantum concept).  The feline is neither alive nor dead until the
radioactive atom is measured by an observer. Although this thought
experiment is impossible to carry out for a number of reasons,
including the fact that the quantum properties of a system tend to
wash out in an object made of many atoms and molecules such as
a cat, the NIST physicists have demonstrated the basic principles
using a single beryllium ion.  The researchers trap the ion with
nonuniform electric fields and cool it to a near standstill.  Laser
pulses then cause the ion to oscillate as a combination of
wavepackets representing two different electronic states.  Additional
laser pulses push apart the two wavepackets to separations of as
much as 80 nanometers, a mesocopic-size scale far bigger than the
normal spatial extent of the ion.  So in this version of Schrodinger's
cat, the ion's electronic state (a quantum property) is linked to (or
"entangled" with)  a mesocopic-scale position (a non-quantum
property). By applying subsequent pulses that bring together the
wavepackets, the researchers detected interference patterns which
provided evidence of the original separation.  Measurements of
Schrodinger cat's states can provide information on how quantum
properties wane with the amount of physical separation between
quantum states.  (C. Monroe et al., Science, 24 May 1996.)

SUPERCONDUCTING TUNNEL JUNCTIONS (STJ), under
development as efficient detectors of x rays, can now also be used
as single-photon detectors at visible wavelengths.  In this regard
they will be welcomed by astronomers who increasingly record
incoming light with charge-coupled device (CCD) arrays.  In
contrast to the silicon-based CCDs, which are insensitive to a
photon's energy (one photon engenders one electron in the
detector), the niobium-based STJ's do discriminate as to energy
(one photon, depending on its energy, can generate thousands of
electrons).  Determining a photon's energy would allow
astronomers to forego filters, which lower the detector's overall
efficiency.  A STJ device developed by an Oxford-Cambridge-European Space Agency (Netherlands) collaboration can detect light
in the wavelength range 200-500 nm with a spectral resolution of 45
nm (this should improve to 20 nm or better).  The STJ can also
determine the photon's time of arrival at the millisecond level, a
property the would be handy for studying fast astronomical
processes such as pulsars.  (A. Peacock et al., Nature, 9 May
1996.)

PHYSICS BACHELOR'S DEGREES. Here are some highlights
from a new AIP report on 1994 degree recipients in the U.S.---the
annual number of degrees continues to decline slightly; more fresh
graduates are looking for jobs rather than heading for graduate
school; for those going on in their studies 89% receive financial
support; women constitute 17% of the degree recipients; median
starting salary was $27,000.  (Patrick Mulvey, 301-209-3076.)